In recent years, the number of LSIs (large scale integrated circuits) mounted in each of electronic systems such as personal computers tends to increase. As a result, in order to stably operate the electronic system, it is necessary to mount on a board many decoupling capacitors adapted for preventing mutual interference between the LSIs. Further, LSIs have been increasing in speed and there are those LSIs whose operating frequencies exceed 1 GHz. On the other hand, there are many cases where low-speed operating LSIs are also still used on the same board. In this case, it is necessary that a plurality of capacitors having different capacitances be combined and mounted on the board for decoupling over a range from low frequency of several tens of kHz to high frequency of approximately several GHz.
In order to satisfy these requirements, there are instances where capacitors exceeding 1000 in number are used, for example, on a server board or the like. This makes component layout on the printed board very difficult.
For solving such a problem, there has been proposed an element called a shield stripline element and having excellent decoupling properties, which takes the place of the capacitor. Such a shield stripline element is disclosed, for example, in Japanese Unexamined Patent Publication No. 2003-101311 (hereinafter, Document 1) or Japanese Unexamined Patent Publication No. 2003-124066 (hereinafter, Document 2).
However, the shield stripline element disclosed in Document 1 or 2 has several problems.
The first problem is that its external shape is large as compared with a conventional chop capacitor or the like. Therefore, not only is it not possible to largely reduce the area occupied by decoupling elements on the printing board, but it cannot be expected that the difficulty of layout is solved.
The second problem is that the decoupling properties degrade when the frequency becomes 100 MHz or more. The main cause of this is that a lead electrode necessary for mounting on a printed board or the like and a conductive polymer used as a material each has a high impedance in a high-frequency range of approximately 100 MHz or more. That is, the lead electrode itself has an inductance. Given that the inductance is L and the frequency is f, its impedance Z is expressed as Z=j2πfL. Accordingly, as the frequency increases, the impedance of the lead electrode increases. Further, the conductive polymer interposed between a dielectric layer and the electrode also decreases in conductivity in the high-frequency range and serves as a parasitic inductance with high impedance. As a result, the decoupling properties degrade.